The initial contact of normal or malignant cells or non-pathogenic, pathogenic or oncogenic viruses with each other and with the external environment is via the external membrane. This contact may lead to any of multiple responses on the part of the cells or viruses involved depending on the nature and biological function of the elements involved. Relatively little is known of these functional characteristics of the external membranes of various cells and viruses. This project is an attempt to characterize certain aspects and properties of the limiting membrane of malignant, transformed and normal cells and the envelope of several viruses. Particular emphasis will be placed on the potentially lytic effector system, complement, and the conditions responsible for its triggering, certain aspects of its interactions with membranes or envelopes and an examination of how the cell or virus deals with it. More specifically, the project is an investigation of the mechanisms involved in antibody independent and dependent triggering of the complement system by lymphocyte and viral membranes, an analysis of the nature of binding of early reactive complement components with biological membranes and an experimental evaluation of repair of complement-mediated membrane damage. A molecular and biochemical approach to these studies will be employed with the intent of description of the sites and reactions involved in these terms.